The interior of the right atrium has a rough anterior part, the atrium proper and a smooth part called the sinus venarum. Also it has an appendage called the auricle. All the large veins open into the smooth part. The opening of the superior vena cava is situated in its upper and posterior part and that of inferior vena cava into its lower part, close to the interatrial septum. The opening of the inferior vena cava is bounded by a fold called the valve of the inferior vena cava. Just to the left of this is the opening of the coronary sinus.